linux-kernel - Re: [BUG 2.6.31-rc1] HIGHMEM64G causes hang in PCI init on 32-bit x86

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Date:	Mon, 29 Jun 2009 05:21:55 -0600
From:	Matthew Wilcox <matthew@....cx>
To:	Mikael Pettersson <mikpe@...uu.se>
Cc:	"H. Peter Anvin" <hpa@...or.com>,
	Grant Grundler <grundler@...isc-linux.org>,
	linux-kernel@...r.kernel.org, linux-pci@...r.kernel.org
Subject: Re: [BUG 2.6.31-rc1] HIGHMEM64G causes hang in PCI init on 32-bit
	x86

On Mon, Jun 29, 2009 at 01:12:05PM +0200, Mikael Pettersson wrote:
> H. Peter Anvin writes:
>  > Grant Grundler wrote:
>  > > On Sat, Jun 27, 2009 at 11:45:24AM +0200, Mikael Pettersson wrote:
>  > > ...
>  > >>   fff00000-fffffffe : pnp 00:09
>  > >> 100000000-1ffffffff : System RAM
>  > >> 200000000-ffffffffffffffff : RAM buffer
>  > >>
>  > >> With 2.6.30 things look similar, except 2.6.30 does not show the
>  > >> last "200000000-ffffffffffffffff : RAM buffer" line.
>  > > 
>  > > BIOS e280 table didn't report that line.
>  > > I expect it's created by arch/x86/kernel/e820.c:
>  > > 1398         /*
>  > > 1399          * Try to bump up RAM regions to reasonable boundaries to
>  > > 1400          * avoid stolen RAM:
>  > > 1401          */
>  > > 1402         for (i = 0; i < e820.nr_map; i++) {
>  > > 1403                 struct e820entry *entry = &e820_saved.map[i];
>  > > 1404                 resource_size_t start, end;
>  > > 1405 
>  > > 1406                 if (entry->type != E820_RAM)
>  > > 1407                         continue;
>  > > 1408                 start = entry->addr + entry->size;
>  > > 1409                 end = round_up(start, ram_alignment(start));
>  > > 1410                 if (start == end)
>  > > 1411                         continue;
>  > > 1412                 reserve_region_with_split(&iomem_resource, start,
>  > > 1413                                                   end - 1, "RAM buffer");
>  > > 1414         }
>  > > 
>  > 
>  > OK, this seems more than a wee bit strange, to say the least.  We
>  > shouldn't be reserving the entire address space; this is legitimate I/O
>  > space.
>  > 
>  > However, the reservation suddenly being improper for the root resource
>  > would definitely make things unhappy...
> 
> Reverting the two e820 changes in 2.6.31-rc1,
> 5d423ccd7ba4285f1084e91b26805e1d0ae978ed and then
> 45fbe3ee01b8e463b28c2751b5dcc0cbdc142d90,
> but keeping the iomem_resource.end cap change, makes 2.6.31-rc1
> work on my HIGHMEM64G machine.
> 
> Seems the e820 and the iomem_resource.end changes are Ok in
> isolation but break when combined.

With the e820 change reverted, what does /proc/iomem look like?

-- 
Matthew Wilcox				Intel Open Source Technology Centre
"Bill, look, we understand that you're interested in selling us this
operating system, but compare it to ours.  We can't possibly take such
a retrograde step."
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